As for conventional diamond lasers, there is an example described in U.S. Ser. No. 673,304. The priority of U.S. Ser. No. 673,304 is claimed in International Patent Pulbication No. WO 86/03347. Reference may also be had to (Optics Letters), Vol. 10, p. 481 (Oct. 1985), in which pulsed laser action is effected at 530 nm using H3 color centers. In said laser, a natural diamond is used.
There has been no example which effects or suggests laser action using H2 color centers. However, properties of H2 centers are described, in "Reports on Progress in Physics", Vol. 42, pp. 1605-1659 (1979). Said "Reports on Progress in Physics" state that H2 color centers are not formed in type Ib diamond, that such H2 centers coexist with H3 centers, and that H2 centers have a low absorption in a natural type Ia diamond.
A conventional method of forming H2 color centers, as described in "Optical Absorption and Luminescence in Diamond", printed in "Reports on Progress in Physics", Vol. 42, p. 1648 (1979), comprises the step of heat-treating, at 627.degree. C., natural Ia type diamond containing not less than 10.sup.19 nitrogen atoms/cm.sup.3. In this case, heating at 227.degree.-327.degree. C. in dark places increases the H2 centers but decreases the H3 centers. Further, with the conventional method, it is impossible to in H2 centers from type IIa and type Ib diamonds.
In this connection, lasers which are capable of operating at varying wavelength in the near infrared region include the F center laser using alkali halide single crystals and the dye laser.
The lasing wavelength of said F center laser is in the ranges of 1400-1600 nm however, laser action is impossible and 2200-3300 nm in the range of 1000-1400 nm laser action is impossible. The wavelength range in which the dye laser oscillates continuously is 330-1050 nm and 1100-1200 nm. The range in which the laser output power is high is 400-800 nm, and the output power in the near infrared region is very low.
Thus, the conventional near infrared lasers have the following drawbacks:
(i) The wavelength cannot be varied, in the region of 1000-1400 nm;
(ii) The output power is very low in a dye laser having a tuning range of 1100-1200 nm.